A. Field of the Invention
The invention relates to the detection of hyperfine particles in a fluid and the optical determination of their type and size distribution. It also relates to the analysis of wear of moving parts, such as jet engine bearings and to the testing of the performance of various lubricants.
B. Prior Art
Frequently it is necessary or desirable to monitor certain characteristics of particles in a fluid, such as particle type (e.g. pure metal, oxide, sulfide, etc.), size, and concentration among others. For example, in connection with machinery having moving parts which reciprocate or rotate with respect to one another, a lubricating oil is generally applied to the moving parts to minimize friction between the parts and attendant wear. In many cases, lubrication does not completely eliminate all wear, however, and material is continuously abraded from the machinery during use. The lubricating oil carries away these abraded particles. Examination of the particles suspended in the oil enables one to monitor operation of the machinery and thereby detect incipient failures. Frequently, the particles are of extremely small size (e.g. having maximum dimensions from a few microns down to a hundredths of microns; these are hereinafter termed "hyperfine").
The concentrations of small amounts of various substances in a fluid are frequently measured by chemical or spectrometric techniques. Both of these are primarily laboratory-type techniques in that they often require expensive and complex equipment which is not readily adapted for in situ measurements. Additionally, these techniques are inadequate for determining characteristics of particles in a fluid, such as particle size distribution, or the rate at which this distribution changes, which I have found to be of great assistance in predicting machinery failures from wearing parts.
Liquid suspensions are also commonly examined with the aid of a microscope to determine characteristics of the particles suspended in them. This is done by transmitting light through the liquid and observing the light reflected or refracted into the microscope by the particles. However, this technique is inadequate for examination of suspensions of hyperfine particles of low concentration (e.g. several parts per million) since they are too small to significantly disturb the wavefront of the light incident on them. Further, even somewhat larger particles are not photographed in suspension without difficulty since their Brownian motion "blurs" the observation, expecially over an extended time period.